Lattice tower

ABSTRACT

This invention relates to lattice tower for actuate under high load conditions, more particularly to lattice towers utilized for wind turbines and other applications comprising three metallic legs arranged in a triangular configuration around a vertical axis of the lattice tower, wherein each metallic leg has a closed cross-section profile, a distance between the center of metallic legs in a bottom portion of the tower is greater than 4 meters, an angle of inclination of a central longitudinal axis of each metallic leg in relation to the vertical axis of the tower is between −1.7 degree and +1.7 degrees, and the height of the lattice tower is greater than 60 meters, a plurality of bracing members and auxiliary bracing members and a support platform disposed at a top portion of the tower.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 14/765,245 titled “LATTICE TOWER”, filed Jul. 31,2015, which is a U.S. National Stage Application under 35 U.S.C. § 371of International Application No. PCT/BR2013/000036, filed Feb. 1, 2013,each of which is hereby incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION (US) Technical Field

This invention relates to lattice tower for actuate under high loadconditions, more particularly to lattice towers utilized for windturbines and other applications.

Background Art

Vertical structures for supporting high loads such as towers or the likeutilized for supporting wind turbines, power transmission lines andother applications are well known in the prior art. The structuraldesigns, components and materials of such vertical structures varydepending upon the application.

One type of vertical structure that has been receiving special attentionin the last decades are the vertical structures for wind turbines orother high loads.

Wind energy has become a very attractive source of energy, both due toan increase in efficiency of the generators and an increase in marketdemand for clean and renewable sources of energy. The increase of theefficiency of the wind energy generators is related to a great effort inenhancing several aspects of the technology, including many issuesrelated to the design and manufacturing of the wind energy generatorcomponents including, among others, the rotor blades, the electricalgenerator, the tower and the control systems.

Most wind turbines used in megawatt applications, nowadays varying inthe range of about 1 MW to 5 MW, have a horizontal-axis wind turbine(HAWT) configuration with a main rotor shaft and an electrical generatorat the top of a tower, and the rotor axis directioned to the inflow ofthe wind with three-blades positioned upwind.

The main advantage of the upwind design is the avoidance of the windshade and resulting turbulence behind the tower. Currently, most oflarge scale wind turbines adopt the upwind design; however, this designhas various drawbacks such as the need of some distance between thetower and the blades due to the bending of the blades and the need of ayaw mechanism to keep the rotor facing the wind. The yaw mechanismusually has a wind sensor associated by an electronic controller to ayaw drive, which includes one or more hydraulic or electric motors and alarge gearbox for increasing the torque, as well as a yaw bearing. Theyaw bearing provides a rotatable connection between the tower and thenacelle of the wind turbines. The yaw mechanism usually includesadditional components, such as brakes that work in cooperation with thehydraulic or electric motors in order to avoid wear and high fatigueloads on the wind turbine components due to backlash during orientationof the rotor according to the wind direction. As the wind turbine willusually have cables that carry the electric current from the electricgenerator down through the tower, the cable may become twisted due tothe rotation of the yaw mechanism. Therefore, the wind turbine may beequipped with a cable twist counter that is associated with the yawmechanism electronic controller in order to determine the need ofuntwisting the cables by the yaw mechanism.

The downwind design, by which the rotor is placed on the lee side fromwhich the wind blows in tower, would in principle avoid the need of ayaw mechanism if the rotor and nacelle have a suitable design that makesthe nacelle follow the wind passively, utilizing the wind force in orderto naturally adjust the orientation of the wind turbine in relation tothe wind. This theoretical advantage is doubtful in large megawatt windturbines because there usually remains a need to untwist the cables ifthe rotor continuously turns in the same direction. In addition, thereare mechanical problems such as fatigue of the components due to strongloads resultant from the sudden changes of the wind direction.Nevertheless, the downwind design still presents an important advantagein regard to the structural dynamics of the machine, allowing a betterbalancing of the rotor and tower. In the case of larger wind turbinerotors, which nowadays have a diameter reaching about 120 meters (about393.6 ft) or more, obtaining more flexibility in the design of the rotorblades is essential.

However, the increase of diameter of the rotor usually involves heavierrotors and the increase of the height of the tower, consequently, mayinvolve the use of additional material, for instance, steel, formanufacturing the tower.

Hence, as a tower usually represents about fifteen to thirty percent ofthe cost of the wind energy generator, there is a great need to obtainhigher and more robust towers at lower costs.

Most large wind turbines manufactured in the last two decades with apower output higher than one megawatt adopt tubular steel towers,commonly referred to as “monopoles”, as the preferred choice. Themonopoles usually taper from the base to the top or close to the top,having modules connected together with bolted flanges. A constraintrelated with monopoles is the road transportation limitations thatrestrict the diameter of the segments. For instance, tubular segmentswith diameters higher than about 4 meters (about 13 feet) may not betransported on roads in many countries.

Lattice towers usually need less material (e.g. less steel) thanmonopoles, but require a higher number of components and boltedconnections. These bolted connections are subject to the varying fatigueloads, hence, they have the disadvantage of higher maintenance needs.

Disclosure Technical Problem

One particular technical problem regarding vertical structures such astowers or the like utilized for supporting high loads such as large windturbine generators is the lack of balancing between the stress andstrain distribution of the vertical and horizontal loads vectors alongthe extension of the vertical structure. Due to this lack of balancing,the tower segments are designed with significant losses of materials insome segments or with assemblies that result in complex manufacturing,transportation and installations requirements.

Other problems to be considered are the low natural frequencies of modesof bending and torsion, and the level of vibration and trepidation thatthe wind causes in the tower.

Likewise, regardless of the upwind or downwind design, if the rotor axisis not substantially positioned to direction of the inflow of the windthere is a so called yaw error angle, causing a lower fraction of theenergy in the wind flowing through the rotor area. In general, thefraction of lost power is proportional to the cosine of yaw error angle.Moreover, the yaw error causes a larger bending torque at the portion ofthe rotor that is closest to the source of the wind, resulting in atendency of the rotor to yaw against the wind and the blades bend backand forth in a flapwise (or flatwise) direction for each turn of therotor. Therefore, on one hand adequate alignment of the wind turbinerotor in relation to the wind is essential for obtaining good windenergy extraction performance and low wind turbines components wear,while on the other hand there is a need for a low cost yaw mechanismwith the advantages of the downwind design.

Technical Solution

To overcome the drawbacks and problems described above and otherdisadvantages not mentioned herein, in accordance with the purposes ofthe invention, as described henceforth, one basic aspect of the presentinvention is directed to a lattice tower for actuate under high loadconditions.

Advantageous Effects

The present invention has several advantages over the prior art. Incomparison with the vertical structures of the prior art, the presentinvention enables a surprising reduction in the weight of the metallicstructure of about 40%, depending on the design requirements of thecase. One of the reasons for such expressive reduction in the totalweight of the structure is that each leg of the vertical structure has astress and strain behavior similar to a monopole, without having therestrictions of the large diameter of the single monopole verticalstructures. The reduction of the weight of the metallic structure isaccompanied by an advantageous reduction of the total costs of thestructure, including the costs of manufacturing, transport andinstallation.

The advantage of weight reduction is accompanied by furthermanufacturing, transportation and installation advantages, as well asavailability of a new class of vertical structures for high and criticalapplications, such as wind energy turbines with a power output higherthan 3 MW with towers higher than 100 meters (higher than 328 feet).

Furthermore, another aspect of one embodiment of the invention allowsthe vertical and horizontal alignment of the rotor, without constantneed of full force of the yaw mechanism, while also absorbing andproviding damping effect for bursts winds or extreme winds.

Furthermore, another aspect of one embodiment of the invention providesa large platform in relation to the size of a standard nacellepermitting the use of alternative tower design with low shadow wind andturbulence for downwind application, resulting in significantflexibility in the design of blades, substantially reducing the costsand improving performance.

DESCRIPTION OF DRAWINGS

The above and other exemplary aspects and/or advantages will become moreapparent by describing in detail exemplary embodiments with reference tothe accompanying drawings, which are not necessarily drawn on scale. Inthe drawings, some identical or nearly identical components that areillustrated in various figures can be represented by a correspondingnumeral.

For purposes of clarity, not every component can be labeled in everydrawing.

FIG. 1 shows a perspective view of one exemplary of a lattice tower forsupporting loads according to one embodiment of this invention.

FIG. 2A is a side view of one exemplary of a lattice tower according toone embodiment of this invention.

FIG. 2B is a partial detailed view of the inclination at (31 and (32angles of the bracing members in relation to the central axis of eachone of the lattice tower legs, according to one embodiment of thisinvention.

FIG. 3A is a top view of the lattice tower, according to one embodimentof this invention.

FIG. 3B is a bottom view of the lattice tower, according to oneembodiment of this invention.

FIG. 4 is a partial schematic exaggerated view of the inclinationbetween the central longitudinal axes, the vertical axis of the towerand the leg's conicity, according to one embodiment of this invention.

FIG. 5A is a side view of one exemplary of a lattice tower according toone embodiment of this invention, serving as reference to show thedifferent configurations of the cross-sections of the tower legs alongits height.

FIG. 5B is a cross-section view of the legs along the third portionlength of the lattice tower (with the inclination and conicityexaggerated, as well as not in scale), according to one embodiment ofthis invention.

FIG. 5C is a partial schematic view of the leg along the third portionlength of the lattice tower (with the inclination and conicity enlargedexaggerated, as well as not in scale), according to one embodiment ofthis invention.

FIG. 5D is a cross-section view of the legs along the second portionlength of the lattice tower (with the inclination and conicity enlargedas well as not in scale), according to one embodiment of this invention.

FIG. 5E is a partial schematic view of the leg along the second portionlength of the lattice tower (with the inclination and conicityexaggerated, as well as not in scale), according to one embodiment ofthis invention.

FIG. 5F is a cross-section of the legs along the first portion length ofthe lattice tower (with the inclination and conicity enlarged as well asnot in scale), according to one embodiment of this invention.

FIG. 5G is a partial schematic view of the leg along the first portionlength of the lattice tower (with the inclination and conicityexaggerated, as well as not in scale), according to one embodiment ofthis invention.

FIG. 6A is a view of one exemplary polygonal cross-sectional shapeaccording to one embodiment of this invention.

FIG. 6B is a view of one exemplary reduced web profile cross-sectionalshape and fairing according to one embodiment of this invention.

FIG. 7 is a detailed view of one exemplary connection of the modules ofthe lattice tower length, according to one embodiment of this invention.

FIG. 8 is perspective view of the support platform with inner tubularinterface to perform similar function as the current technique forelongated nacelles, according to one embodiment of this invention.

FIG. 9 is a lateral view of the support platform with inner tubularinterface, according to one embodiment of this invention.

FIG. 10 is a frontal view of the support platform with inner tubularinterface, according to one embodiment of this invention.

FIG. 11 is a posterior view of the support platform with inner tubularinterface, according to one embodiment of this invention.

FIG. 12 is a plan view of the support platform with an inner tubularinterface for passageway for cables according to one embodiment of thisinvention.

FIG. 13A is a perspective view of one exemplary of a lattice tower withsupport platform with inner tubular interface related to a wind energyturbine, according to one embodiment of this invention.

FIG. 13B is also a perspective view of the solid model of one exemplaryof a lattice tower with support platform with inner tubular interfacerelated to a wind energy turbine, according to one embodiment of thisinvention.

FIG. 14 is a frontal view of one exemplary of a lattice tower withsupport platform with inner tubular interface related to a wind energyturbine, according to one embodiment of this invention.

FIG. 15A is a lateral view of one exemplary of one embodiment of thisinvention wherein the load is an upwind turbine assembly with elongatednacelle.

FIG. 15B is a lateral view of one exemplary of one embodiment of thisinvention wherein the load is an downwind turbine assembly withelongated nacelle.

FIG. 16A is a lateral view of one exemplary of one embodiment of thisinvention wherein the load is a upwind turbine assembly with elongatednacelle.

FIG. 16B is a lateral view of one exemplary of one embodiment of thisinvention wherein the load is a downwind turbine assembly with elongatednacelle.

FIG. 17A is a top view of one exemplary of one embodiment of thisinvention wherein the load is a upwind turbine assembly with elongatednacelle.

FIG. 17B is a top view of one exemplary of one embodiment of thisinvention wherein the load is a upwind turbine assembly with elongatednacelle, rotated by 90° with respect to the configuration of FIG. 17A.

FIG. 17C is a top view of one exemplary of one embodiment of thisinvention wherein the load is a upwind turbine assembly with elongatednacelle, rotated by 180° with respect to the configuration of FIG. 17A.

FIG. 18A is a top view of one exemplary of one embodiment of thisinvention wherein the load is a upwind turbine assembly with elongatednacelle.

FIG. 18B is a top view of one exemplary of one embodiment of thisinvention wherein the load is a upwind turbine assembly with elongatednacelle, rotated by 90° with respect to the configuration of FIG. 18A.

FIG. 18C is a top view of one exemplary of one embodiment of thisinvention wherein the load is a upwind turbine assembly with elongatednacelle, rotated by 180° with respect to the configuration of FIG. 18A.

FIGS. 19A and 19B show the Table I corresponding to the dimensioningspreadsheet of a tower in steel only according to one embodiment of thepresent invention.

FIGS. 20A and 20B show the Table II corresponding to the dimensioningspreadsheet of a tower in steel reinforced with concrete according toone embodiment of the present invention.

FIG. 21 shows in the Table III the summary of the comparison betweenthree towers: the monotubular tower, the lattice tower in steel, and thelattice tower in steel reinforced with concrete.

FIG. 22 is a frontal view of another exemplary of a support platformrepresented as a yaw support structure according to one embodiment ofthis invention.

FIG. 23 is a perspective view of another exemplary of a support platformrepresented as a yaw support structure according to one embodiment ofthis invention.

FIG. 24 is a plan view of another exemplary of a support platformrepresented as a yaw support structure according to one embodiment ofthis invention.

FIG. 25 is a detailed superior view of another exemplary of a supportplatform represented as a yaw support structure according to oneembodiment of this invention.

FIG. 26 is a lateral view of another exemplary of a support platformrepresented as a yaw support structure according to one embodiment ofthis invention.

FIG. 27 is a perspective view of another exemplary of a support platformrepresented as a yaw support structure with two interfaces according toone embodiment of this invention.

FIG. 28 is a plan view of another exemplary of a support platformrepresented as a yaw support structure with two interfaces according toone embodiment of this invention.

FIG. 29 is a plan view of another exemplary of a support platformrepresented as a yaw support structure with two interfaces according toone embodiment of this invention.

FIG. 30 is a lateral view of another exemplary of a support platformrepresented as a yaw support structure with two interfaces according toone embodiment of this invention.

FIG. 31 is a perspective view of another exemplary of a support platformrepresented as a structure with two interfaces according to oneembodiment of this invention.

FIG. 32 is a plan view of one exemplary of a support platform showingthe connection of the yaw support platform in the top of the latticetower by bracing members.

EXPLANATIONS OF LETTERS AND NUMERALS

Numerals Explanation of numerals 10 Lattice tower 11 Metallic legs 12Vertical axis of the tower 13 Bracing members 13a Auxiliary bracingmembers 14 Support platform 16 Central longitudinal axis 17a Top portion(of lattice tower assembled) 17b Base portion (of lattice towerassembled) 18 Flange of linkage 20 Module 21a First portion 21b Firstlegs 22a Second portion 22b Second legs 23a Third portion 23b Third legs24 Clearance upwind distance 25 Clearance downwind distance 26 Channelwith reduced web 27 Oblong aerodynamic profile 30a A frusto-conicalcross-section first leg 30b Bottom portion of first leg 30c Top portionof first leg 31a A frusto-conical cross-section third leg 31b Topportion of third leg 31c Bottom portion of third leg 40 Support platformwith inner tubular interface 41 Platform leg 42 Inner tubular interface43 Yaw mechanism support structure 44 Rotor blades 45 Electric generator46 Body 47 Upper surface 48 Lower surface 49 Circular track 50 Yawrotating mechanism 51 First axis that is perpendicular to the uppersurface of the platform 52 Longeron of turbine support platform 53 Firstend turbine support platform frame 54 Second end turbine supportplatform frame 55 Second axis that is perpendicular to the first axis 56Wind energy turbine with elongated nacelle 57 Yaw actuator 58 Wheels 58aDampener element 60 Wind direction 61 Interface 61a Second Interface 63Gearbox 64 Passageway for cables 65 Shaft 66 Furling mechanism

MODES FOR INVENTION

Hereinafter, exemplary embodiments will be described with reference tothe attached drawings. Like reference numerals in the drawings denotelike elements. While exemplary embodiments are described herein, theyshould not be construed as being limited to the specific descriptionsset forth herein; rather, these embodiments are provided so that thisdisclosure will be thorough and complete. In the drawings, the sizes ofcomponents may be exaggerated or made smaller for purposes of clarity.

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including”, “comprising”, “having”, “containing” or “involving”, andvariations thereof used in this description, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems. The dimensions as recited herein are merely exemplary and otherdimensions may be used in conjunction with the exemplary embodiments aswould be understood by one of skill in the art.

FIG. 1, which is on an approximate scale, shows a perspective view of anexemplary lattice tower 10, higher than 60 meters (about 197 ft),according to one embodiment of the present invention. The lattice tower10 is formed by three metallic legs 11, configurated in metallic shells,which have their central longitudinal axis 16 inclined in relation tothe vertical axis 12 of the lattice tower 10. At the foundation, in baseportion 17 b, the three legs 11 are arranged in an equilateraltriangular configuration around the vertical axis 12 of the tower, in adistance greater than 4 meters measured between the centers 16 of eachleg of the lattice tower 10. The metallic legs 11 have a substantiallycircular and closed cross-section and are connected to each other alongthe lattice tower 10 structure height by a plurality of bracing members13 and auxiliary bracing members 13 a which are arranged diagonally andhorizontally, respectively. A support platform 14 is disposed at the topportion 17 a of the lattice tower 10 serving as an interface forsupporting loads like wind turbine, electric power transmission lines,telecommunications systems, and other applications.

FIG. 2A is a side view of one exemplary embodiment of the inventionshowing the silhouette (the vertical profile) of the lattice tower 10wherein its metallic legs 11 are divided in three portions: a firstportion 21 a, a second portion 22 a and a third portion 23 a. The firstportion 21 a and the third portion 23 a have two inverted right circulartruncated conical shape which are interconnected, at their narrow end,by the second portion 22 a which has cylindrical shape of smallerdiameter. All portions are aligned through its central longitudinal axis16.

FIG. 2A shows also a plurality of bracing members 13 and auxiliarybracing members 13 a, arranged diagonally and horizontally,respectively, and attached to the metallic legs 11 of the lattice tower10 at regular intervals along the length of the metallic legs 11, havingthe function of providing resistance to lateral and/or rotationaldisplacement to stiffen the lattice tower 10. The construction of saidbracing members 13, especially the diagonal ones which are constructedin the interior of the lattice tower 10 in a X-shaped format, are madeup in a configuration inclined in a β1 and β2 angle in relation to thecentral longitudinal axis 16 of each metallic leg 11, as depicted inFIG. 2B. Although the angles β1 and β2 are not necessarily identicalsand may vary according to the position of the bracing member 13 alongthe height of the lattice tower 10, said angles have values betweenabout 30 and 60 degrees, preferably around 45 degrees. The side viewshown in FIG. 2A, illustrates also the three metallic legs 11 of thelattice tower 10 wherein the metallic legs are divided in three portionsalong its length, each portion formed preferentially by at least onemodule or module 20. This division is according to the assembly of thetower considering its inverted truncated conical portions andcylindrical portion, as well as is intended to provide a betterunderstanding of its design function, as previously described.

The first portion 21 a is formed by three first legs 21 b, the secondportion 22 a which is formed by second legs 22 b, each second leg 22 b,preferentially, is linearly aligned with and coupled to a correspondingfirst leg 21 b of the first portion 21 a. A third portion 23 a includesthree third legs 23 b, each third leg 23 b, preferentially, is linearlyaligned with and coupled to a corresponding second leg 22 b of thesecond portion 22 a.

The FIG. 3A is a top view of the lattice tower, according to oneembodiment of this invention, which helps to understand the threemetallic legs 11 shape having two inverted right circular truncatedconical shape which are interconnected, at their narrow end.

As depicted in the FIG. 3B, the three metallic legs 11 are arrangedsymmetrically at equal angles around a vertical axis of the tower 12 andwith equal distances “d” between each other, in a triangularconfiguration, preferably in an equilateral configuration. Eventually,small variations due to the geometric dimensioning and tolerances thatmay be considered for the assembly, for instance due manufacturing orland and foundation limitations. The distance “d” between the centrallongitudinal axes 16 of each leg in the bottom portion 17 b of thelattice tower base when fixed to the ground, is greater than 4 meters(about 13.12 ft).

FIG. 4 is a partial schematic view of the inclination between thecentral longitudinal axis and the vertical axis of the tower, accordingto one embodiment of this invention. The scale of this view has beenexaggerated for clarity. In the example, the central longitudinal axis16 of each metallic leg 11 can be inclined until an angle (0) of 1.7degree in relation to the vertical axis of the lattice tower 10 andaround the central longitudinal axis 16 in accordance to thecharacteristics of load it is intended for, like wind turbine, electricpower transmission lines, and other applications.

Additionally, the lattice tower 10 is configured to provide a generalaspect of the vertical profile (silhouette) wherein in an exaggeratedscale the tower would have an hourglass-shape that defines the lowerportion of the tower relatively broad at its lower end (distance “Ab” inthe base portion 17 b) and relatively narrow at its upper end (distance“At” in the top portion 17 b), as depicted in FIG. 4, but in fact in atrue scale the general aspect of the vertical profile (silhouette) wouldappear to be linearly vertical at right angles. Furthermore, as depictedfrom FIG. 04, the distance “At” is, preferentially, lower than thedistance “Ab”.

The tower configuration shown in FIG. 4, is suitable to ensure a properdistribution of the efforts that are caused by loading the lattice tower10 once this type of silhouette allows reinforcing the top portion 23 aof the metallic legs 11 with diameters and thicknesses larger thannormally found in prior art. Also, this configuration allows a doubleeffect in terms of structure once that increases the strength and thenatural frequency of the tower and at the same time reduces itsmanufacturing, transport and installation costs. In addition, theportions 22 a and 23 a, as depicted in FIG. 2A, are especially suitableto reduce the aerodynamic turbulence in the region where the rotorblades passes, allowing the use of a downwind configuration as shown inFIG. 16B. The downwind design, as shown in FIG. 16B, is veryadvantageous because the clearance 24 is not a problem while the blade44 bends deviating from the lattice tower 10 in this wind condition.

In the case of the upwind design, as shown in FIG. 15A, as the tower ismuch stronger than conventional towers, it is possible to increase theclearance upwind distance 24 reducing the chance of a rotor bladestriking the tower.

The design of the lattice tower 10 is made to support dynamic loads onthe support platform 14 at the top portion of the tower 17 a that causereaction forces and moments in a base portion 17 b of the lattice tower10, that be above than 10 (ten) times greater that reaction forces andmoments caused by wind loads on the lattice tower itself.

For reference and as an example of a load, a large scale wind turbineavailable commercially with nominal output of 7.58 MW has an approximateweight of the foundation of the turbine tower about 2,500 ton, the toweritself 2,800 ton, the machine housing 128 ton, the generator 220 ton,and the rotor (including the blade) 364 ton. Accordingly, the dynamicsloads on the support platform caused by the generator and the rotor aremuch higher than maximum wind loads imposed specifically in the toweritself. Usually, a tower for supporting only standard telecommunicationantennas would be subject to completely different loads, because in thiscase the wind loads in the tower are usually higher than the loadscaused by the telecommunication antennas in the top of the tower.

The metallic legs 11 are designed in truncated conical portions in thefirst portion 21 a and in the second portion 23 a, and in cylindricalportion in the second portion 22 a so that the diameter variationremains smooth throughout the metallic legs 11 length avoidingdiscontinuities that can cause areas of stress concentration which canalso cause air bubbles during concreting, in case of adoptingcombinations of different materials in the metallic legs 11construction.

Additionally, the conicity of the column axle envelope of the latticetower 10 is preferably constant and can also be adjusted in order tocompensate the variable conicity of the metallic legs 11, resulting inbracing members 13 that are identical, with the same length, diameterand thickness over the entire height of the lattice tower 10. Thispossibility allows standardizing the length of such bracing members,reducing the cost of their production and facilitating the assembly atsite once, among others advantages, it will not be need to numberingthem.

FIG. 5A is a side view of one exemplary of a lattice tower 10 accordingto one embodiment of this invention, serving as reference for showing ina schematic way the different configurations of the cross-sections ofthe tower legs along its height H. In the exemplary embodiment theoutside diameter “D” to thickness “t” and ratio (D/t) of each metallicleg 11 is greater than 30.

FIGS. 5B, 5D and 5F are views of cross-section of the legs along theportions length of the lattice tower 10, said cross-sections are closedsections, according to one embodiment of this invention.

As shown in FIGS. 5B and 5C, schematically adapted, preferentially oneof the third legs 23 b has also a frusto-conical cross-section 31 a anda top portion 31 b at least one third leg 23 b has a larger diameterthan the bottom portion 31 c of the at least one third leg 23 b.

The second portion 22 a is formed by second legs 22 b having acylindrical structure, as depicted schematically in FIGS. 5D and 5E.Thus, the diameter of each respective third leg 23 b of the thirdportion 23 a is larger than the diameter of each respective second leg22 b in the second portion 22 a.

Additionally, as shown schematically in the FIGS. 5F and 5Gpreferentially at least one of the first legs 21 b has a frusto-conicalcross-section 30 a and a bottom portion 30 b of the at least one firstleg 21 b has a larger diameter than a top portion 31 b of the at leastone first leg 21 b.

Preferentially, the metallic legs 11 have a circular closedcross-section as shown in the FIGS. 5B, 5D and 5F. Alternatively, themetallic legs 11 can also be designed in a shape having, for example, apolygonal cross-sectional shape provided that an aerodynamic fairing,provided that the frusto-conical shape is kept, as depicted in FIG. 6A.

The polygonal cross-sectional shape is shown in FIG. 6A as being,preferentially at least a dodecagon, but it is understood that it couldbe formed into other polygonal shapes, such as a tridecagon,tetradecagon, and so on, according to the suitable construction.

The FIG. 6B illustrates another example of cross-sectional shapeembodiments, preferably used as a profile for the bracing members 13 andauxiliary bracing members 13 a, wherein a channel section with reducedweb 26 is covered by a fairing with an oblong aerodynamic profile 27.The function of the fairing is to cover the channel section, so that thesaid section profile remains closed, enhancing the aerodynamic behaviorof the metallic section with a low cost material of easy formation, suchas polymers, composite materials or other materials, as depicted in FIG.6B. The fairing is intended to minimize turbulence caused by the windand can be designed, alternatively, as example, into another aerodynamicsuitable shapes, which may also include dimples or waves (not shown inthe FIG. 6B) on the surface to generate tiny eddy currents over whichair can flow smoothly, reducing turbulence and improving aerodynamicperformance.

Beyond the metallic material applied for the construction of saidmetallic legs 11, for instance steel, they can also be constructed withmetallic materials associated with composite materials, or compositematerial with reinforced concrete, or composite material withpre-stressed concrete, or combinations thereof; for example, themetallic legs 11 can be filled with reinforced concrete forreinforcement of the structure. As the vertical structures for thepreferred applications, such as wind energy generators, are usually veryhigh, for instance higher than 60 meters, each metallic leg 11 willusually be fabricated in separated segments that are joined togetherduring installation on the site. This means a combination of materialsalong the length of the lattice tower 10 like, for example and notlimited to: the first portion 21 a manufactured together withpre-stressed concrete, the second portion 22 a manufactured togetherwith concrete material with reinforced concrete and the third portion 23a manufactured together with composite materials, or other suitablematerials combinations.

As example of one embodiment of this invention, the coupling betweenportions 21 a, 22 a and 23 a as well as between modules 20 of everyrespective portion is done by using flange 18 coupling, as depicted inFIG. 7.

The bracing members 13 and the auxiliary bracing members 13 a arepreferentially cylindrical shaped, or channel sections (U) with anoblong fairing, and with substantially similar or equal length along theentire height of the lattice tower 10, because with the largest amountof equal parts reduces manufacturing costs and facilitates assembly.

Although the skilled in the art usually adopt for the bracing diagonalmembers and horizontal bars the standard sections commonly used for thepurpose of constructing lattice towers, they can be advantageouslysubstituted by bracing members 13 and auxiliary bracing members 13 ahaving at least one channel section wherein the length of the channelweb is smaller than the length of the channel legs as the ones describesin the WO 2010/076606A1, which specification is incorporated herein byreference.

Accordingly the bracing members 13 or auxiliary bracing members 13 a canbe constructed with a closed cross section, or by using a compositematerial, or by using a metallic bracing member reinforced with acomposite material, or metallic bracing member with closed cross sectionfilled with concrete, or other suitable combinations thereof.

The exemplary embodiment shown in FIGS. 8 to 12 illustrate how the load,in the case of a wind energy turbine, can be supported atop the saidlattice tower 10 through a support platform with an inner tubularinterface 40 that is, in turn, coupled to the lattice tower structure 10by each platform leg 41 with each respective third leg 23 b of the thirdportion 23 a.

The support platform with inner tubular interface 40 is formed by threeplatform legs 41, each platform leg coupled to a respective third leg 23b of the third portion 23 a and an inner tubular interface 42 coupled tothe three platform legs 41, as depicted in FIGS. 8 to 12. In the case ofsupporting a wind turbine, the inner tubular interface is formed by asteel tube and is fixed on the support to allow connection with thenacelle, using the state of the art in terms of nacelle fixation.

In the exemplary embodiment shown in FIGS. 13A and 13B, a wind energyturbine with elongated nacelle 56 is coupled to the lattice tower 10, atits top. Thus, as the lattice tower gives less wind shade than a tubularsteel tower (monopole), the said lattice tower can be arranged to anupwind or downwind design, in accordance with the wind direction 60 anddepending upon the suitable application or construction, as depictedrespectively in FIGS. 14 to 18B.

For illustrative and exemplificative purposes, not limiting the presentinvention, the FIGS. 19A and 19B show the Table I which is adimensioning spreadsheet of an exemplary embodiment of the lattice tower10 with 138 meters high (about 453 ft), using only metallic legs andbracing members without a composite material reinforcement. Thedimensioning spreadsheet shows up the essential dimensions of thestructure of the exemplary lattice tower 10 starting from the quantityof modules 20 as well as their height wherein the modules 20 areconnected together form the lattice tower 10 high.

FIGS. 20A and 20B show the Table II which is also a dimensioningspreadsheet of an exemplary embodiment of the lattice tower 10 which is138 meters high (about 453 ft), wherein the legs and bracing membersinclude reinforced concrete.

In the embodiments of described in the Tables I and II in the FIGS. 19A,19B, 20A and 20B the central longitudinal axes 16 of the metallic legs11 are inclined with less than 0.35 degrees in relation to the verticalaxis of the tower 12. The metallic legs 11 have variable conicity,wherein their diameter starts with 1,000 mm (about 3.281 ft) at the basedecreasing to 510 mm (about 1.673 ft) at 84 meters high (about 275.5 ft)(relating to the first portion 21 a already shown in FIG. 2A); keeps upthe diameter with 510 mm (about 1.673 ft) up to 120 meter high (about393.6 ft) (relating to the cylindrical second portion 22 a already shownin FIG. 2A). Thereafter the conicity of the metallic legs 11 has thesame value as the first portion 21 a, but in a reversed way, and thediameter of the metallic legs 11 increases to 598 mm (about 1.960 ft) atthe top of lattice tower 10 in 138 meters high (about 452.6 ft).

The thicknesses of the legs modules 20 are those normally available inthe market standards. The thickness of the bracing member 13 and theauxiliary bracing members 13 a was calculated to withstand stresses onthe base portion 17 b of the lattice tower 10. The connections systemsof the bracing members 13 and of auxiliary bracing members 13 a with themetallic legs 11 of the lattice tower 10 as well as among themselves,are made of steel and weight about 9.7 tons.

In the exemplary embodiment shown in FIG. 13A, the lattice tower 10 hasabout 0.19 degrees of conicity to compensate the variable conicity ofthe metallic legs 11. The conicity of the lattice tower 10 is constantalong its vertical axis 12, and the longitudinal central legs axis 16 islinear and concentric to the axle of the portions 21 a, 22 a and 23 a,for not generating points of stress concentration.

Therefore, due to the shape of the lattice tower 10 as well as thestructural performance and behavior it is obtained a surprisingreduction in the total cost of the structure, beside the increase offrequency if comparing with a standard monopole tower, normally used forloading wind turbine, as depicted bellow in the Table III. Costs wereestimated on a relative currency, covering the costs of materials,manufacturing, logistics and manpower, not considering the cost ofspecial transportation required by components with large dimensions orweights. Metallic legs 11, bracing members 13 and auxiliary bracingmembers 13 a may be fabricated by any suitable metallic material, forinstance, steel. A high strength low-alloy structural steel ispreferred, and for the comparison shown, the properties of the steelpreferably used are the following: yield strength (fy) is about 3,806kgf/cm²; young's modulus (E) is about 2,100,000 kgf/cm² and density isabout 7,850 kgf/m³. Concrete used has about the following properties:strength (fck) is 510 kgf/cm²; young's modulus (E) is 343,219 kgf/cm²and density is 2,300 kgf/m³. The embedded steel bars of the reinforcedconcrete have about the following properties: yield strength (fy) is5,000 kgf/cm²; young's modulus (E) is 2,100,000 kgf/cm² and density is7,850 kgf/m³.

The FIG. 21 shows the Table III corresponding to the lattice tower 10 insteel only, taking as reference for the comparison and named here asTA1, for wind turbines installed in a high greater than 60 meters (about196.8 ft), is lower cost, of simpler logistics and better spectrum ofnatural frequencies than a monopole, also in steel and named here asTM1, considering an equivalent resistance. The manufacturing cost of thelattice tower 10 is reduced to 1/3 of the cost of the monopole.Considering a lattice tower 10 wherein is used a combination ofmaterials, like steel and reinforced concrete named here as TAC1, thecost is reduced to 1/5 of the monopole TM1, as also depicted in theTable III.

The frequency of the first mode increases from 0.151 Hz, for themonopole tower TM1, to 0.297 Hz, for the TA1. The frequency of 0.297 Hzis out of the frequency range of the rotor blades of a wind turbine. Forthe lattice tower TAC1 wherein is used a combination of materials in thelegs and bracing members, the frequency rises to 0.381 Hz. It also showsthat by changing steel by mixed materials of the same resistance, forexample, reinforced concrete, the cost of the TAC1 decreases even moreat the same time the frequency spectrum is improved. For TAC1, thefrequency of the first mode increases to 0.381 Hz and the cost isreduced approximately 40% in relation to the cost of the TA1.

The Table III summarizes the comparison between the three technologiesstudied. The lattice tower TAC1 in steel and reinforced concrete has thefollowing advantages:

1) Lower Cost: it costs about 20% of monopole TM1 and about 61% alattice tower TA1 in steel only;

2) It has natural frequency of 0.387 Hz, about 28% higher than thelattice tower TA1 in steel and about 152% higher than the monopole TM1;

3) Transport is simpler and lower cost: The concrete is of lower costtransport and can be obtained easily nearby of the most sites ofinstallations, thus the more expensive cost for transporting is for thesteel. The tower TAC1 used 99.2 tons of steel, considering the steelused in the shells of the legs as well as for reinforcing the concreteand for the flanges. This value is 59% of a TA1 tower which has 167.0tons and is 25% the mass of the monopole tower TM1, with 402.5 tons. Forthe monopole tower TM1 the cost is even higher, because it is necessaryspecial transporting system for tubes of 4 meters diameter (13.123 ft)with 12 or 24 meters of length (about 39.4 or 78.7 ft of length).

The lattice tower also presents an equivalent diameter from 1.6 to 1.8meters (about 5.245 to 5.905 ft) with indices of exposed area rangingfrom 13.5% to 15.5%, in the tower height achieved by the length of therotor blades. As also the metallic legs 11 of the tower are distributedalong a distance of 12 meters (about 39.4 ft) between their centrallongitudinal axes 16, the turbulence caused by the tower is small, whichallows its use also to downwind configurations. This setting is morecritical in the tower like monopoles in steel or concrete.

The use of rotor downwind brings numerous advantages to the turbine. Inthis condition the drag and centrifugal force helps reduce the moment atthe blade root by approximately 50%, thereby reducing by 50% the weightof the blades and the hub. Thus it is less weight to be balanced in thenacelle. By having a lower moment of inertia, the azimuth control systemis lighter and lower cost. These and other advantages lead to reducedfinal weight atop the tower in 30 to 40%. Less weight on top implieshigher natural frequencies, further improving the performance of towerin steel and reinforced concrete. Consequently, by these surprisingeffects, a significantly more economical tower is obtained, as it issummarized in the TABLE III, as depicted in FIG. 21.

Further, in another exemplary embodiment as shown from FIGS. 23 to 31,the support platform with inner tubular interface 40 is alternativelysubstituted or complemented with a yaw mechanism support structure 43which is also provided to support a wind energy turbine with elongatednacelle 56, which have a plurality of rotor blades 44 operativelycoupled to gearbox 63 and the electric generator 45 by a shaft 65.

The yaw mechanism support structure 43 is formed by a body 46, an uppersurface 47, a lower surface 48 and a preferentially circular track 49,defined, also preferentially, close to the perimeter of the uppersurface 47 of the yaw mechanism support structure 43.

Additionally, as depicted in FIG. 23, a yaw rotating mechanism 50 iscoupled to the support platform at a position, preferentially centeredwithin the circular track 49 and extending above the upper surface 47 ofthe support platform. Thus, the yaw rotating mechanism 50 is configuredto rotate about a first axis 51 that is, preferentially, perpendicularto the upper surface of the support platform. Further, the yaw rotationmechanism 50 is coupled to longeron of turbine support platform 52 bymean of a furling mechanism 66. In addition, a passageway for cables 64(shown in FIG. 24), for example, power cable, is defined in the yawrotating mechanism 50. By keeping cables internal to the axis of yawrotating mechanism 50 is avoided to get the cables pinched in otherparts of the mechanism, thereby avoiding wear on the cables.

FIG. 24 shows the longeron of turbine support platform 52 having a firstend 53 and a second end 54 spaced apart from the first end by a distanceof at least one radius of the circular track 49, the longeron of turbinesupport platform 52 being pivotally coupled to the yaw rotatingmechanism 50 to allow the longeron of turbine support platform 52 topivot about a first axis 51 that is substantially perpendicular to thesecond axis 55 and substantially parallel to the upper surface 47 of thesupport platform, the longeron of turbine support platform 52 beingconfigured to support at least the weight of the plurality of rotorblades 44 and the electric generator 45 of the wind energy turbine withelongated nacelle 56 mounted thereto.

FIGS. 24 to 26 show the interface 61 disposed proximate the second end54 of the longeron of turbine support platform 52 and between thelongeron of turbine support platform 52 and the substantially circulartrack 49, the interface 61 being configured to provide for the secondend 54 of the longeron of turbine support platform 52 to move along thesubstantially circular track 49 to provide adequate yaw to the winddirection 60. Additionally, the interface 61 is provided with a yawactuator 57 wherein a yaw locking mechanism (not shown) is incorporated.

The interface 61 is represented by at least two wheels 58,preferentially six to transfer turbine loads to the track 49 while thewind turbine is pivoting around the yaw rotating mechanism 50, accordingto one embodiment of this invention. Alternatively, the interface 61 maybe provided with, for example, a pinion gear and a toothed track.Additionally, the wheels 58 are covered by a dampener element 58 aprovided for absorption of vibration which may be caused the wind 60.The dampener element 58 a, incorporated into the wheels 58 of the saidinterface 61, is, for example, based on an elastomeric material.

A second interface 61 a is provided at the first end 53 of the turbinesupport platform frame 52. The second interface 61 a has the samefunction and elements of the interface 61 and is symmetricallypositioned in relation to the yaw mechanism rotating support 50 toensure suitable loading distribution of the wind energy turbine elementsalong the platform as well as to reduce furling rotation which may becaused by the wind force.

This design allows ensuring the wind energy turbine 56 with elongatednacelle is producing the maximal amount of electric energy at all times,by keeping the rotor blades 44 in an optimal positioning into the windas the wind direction changes. Further, the yaw mechanism supportstructure 43 provides better weight distribution of the load along itssecond axis 55, thus reducing an asymmetric load along the structure ofthe yaw mechanism support structure 43 and the lattice tower 10 whichmay be caused by the multidirectional flowing of wind.

FIGS. 27 to 31 illustrate another exemplary embodiment wherein the shaft65 is shorter than the exemplary embodiment shown in FIGS. 22 to 26.

FIG. 31 is a perspective view of one exemplary of a support platformwherein the yaw rotation mechanism 50 is directly coupled to longeron ofturbine support platform 52 without using a furling mechanism 66.

FIG. 32 is a plan view of one exemplary of a support platform,representing, for example as the one described in FIG. 23 or 26, showingthe connection of the yaw support platform atop the lattice tower 10 bybracing members, preferentially, by six bracing members, symmetricallyarranged below the lower surface 48 of the yaw support structure 43.

While exemplary embodiments have been particularly shown and described,various changes in form and details may be made therein by a personskilled in the art. Such changes and other equivalents are also intendedto be encompassed by the following claims.

1. A lattice tower for supporting loads comprising: three metallic legs arranged in a triangular configuration around a vertical axis of the lattice tower, wherein each metallic leg has a closed cross-section profile, a distance between centers of metallic legs in a bottom portion of the tower is greater than 4 meters, an angle of inclination of a central longitudinal axis of each metallic leg in relation to the vertical axis of the tower is between −1.7 degree and +1.7 degrees, and a height of the lattice tower is greater than 60 meters; a plurality of bracing members; and a support platform disposed at a top portion of the tower.
 2. The lattice tower of claim 1, wherein the angle of inclination of the central longitudinal axis of each metallic leg in relation to the vertical axis of the tower is between −1.7 degrees and +1.7 degrees but does not include 0 degrees.
 3. The lattice tower of claim 1, wherein the closed cross-section profile of each metallic leg is substantially circular.
 4. The lattice tower of claim 1, wherein said lattice tower is configured to support dynamic loads on the support platform at the top portion of said lattice tower that cause reaction forces and moments in a base portion of the tower that are more than 10 times greater than reaction forces and moments caused by wind loads on the lattice tower.
 5. The lattice tower of claim 1, wherein said tower is vertically divided in three portions, each portion comprising at least one module, and wherein the three portions comprise: a first portion comprising three first legs; a second portion comprising three second legs, each second leg linearly aligned with and coupled to a corresponding first leg of the first portion; and a third portion comprising three third legs, each third leg linearly aligned with and coupled to a corresponding second leg of the second portion.
 6. The lattice tower of claim 5, wherein the second legs comprise cylindrical structures.
 7. The lattice tower of claim 5, wherein a coupling between portions and between modules of a respective portion comprises a flange coupling.
 8. The lattice tower of claim 1, wherein an outside diameter to thickness ratio (D/t) of each metallic leg is greater than
 30. 9. The lattice tower of claim 1, further comprising auxiliary bracing members, wherein the bracing members are arranged diagonally and the auxiliary bracing members are arranged horizontally.
 10. The lattice tower of claim 1, wherein the bracing members are inclined between 30° and 60° angle in relation to a central axis of each leg.
 11. The lattice tower of claim 1, further comprising auxiliary bracing members, wherein the bracing members or the auxiliary bracing members comprise at least one channel section including a channel web and channel legs, wherein a length of the channel web is smaller than a length of the channel legs.
 12. The lattice tower of claim 1, further comprising auxiliary bracing members, wherein at least one bracing member or one auxiliary bracing member has a closed cross section.
 13. The lattice tower of claim 1, further comprising auxiliary bracing members, wherein the bracing members or the auxiliary bracing members comprise at least one bracing member or one auxiliary bracing member including a composite material.
 14. The lattice tower of claim 1, further comprising auxiliary bracing members, wherein the bracing members or the auxiliary bracing members comprise at least one metallic bracing member or one auxiliary bracing member reinforced with a composite material.
 15. The lattice tower of claim 1, wherein the load is one of a downwind turbine and an upwind turbine.
 16. The lattice tower of claim 1, wherein at least one leg and/or bracing member comprises an aerodynamic fairing.
 17. The lattice tower of claim 5, wherein the support platform comprises three platform legs, each platform leg coupled to a respective third leg of the third portion, and an inner tubular interface coupled to the three platform legs.
 18. The lattice tower of claim 1, further comprising a yaw mechanism support structure to support a wind energy turbine with an elongated nacelle having a plurality of rotor blades operatively coupled to an electric generator, said yaw mechanism support structure comprising: a second support platform having a body, an upper surface, and a lower surface; a circular track defined close to a perimeter of the upper surface of the said yaw mechanism support structure; a turbine longeron support frame having a first end and a second end spaced apart from the first end by a distance of at least one radius of the circular track, the turbine longeron support frame being pivotally coupled to the yaw mechanism support structure, the yaw mechanism support structure being perpendicular to the vertical axis and parallel to the upper surface of the yaw mechanism support structure, the turbine longeron support frame being configured to support at least a weight of the plurality of rotor blades and the electric generator of the wind energy turbine with the elongated nacelle mounted thereto; and at least an interface disposed proximate the second end of the turbine support frame and between the turbine longeron support frame and the circular track, the interface being configured to provide for the second end of the turbine support frame to move along the circular track to provide adequate yaw to the wind direction.
 19. The lattice tower of claim 18, wherein a rotating mechanism including a furling bearing is coupled to the yaw mechanism support structure at a position substantially centered within the circular track and extending above the upper surface of the yaw mechanism support structure, the yaw mechanism rotating support being configured to rotate about a first axis that is perpendicular to the upper surface of the yaw mechanism support structure.
 20. The lattice tower of claim 18, wherein a yaw rotating mechanism is connected directly to the turbine longeron support frame and is coupled to the yaw mechanism support structure at a position substantially centered within the circular track and extending above the upper surface of the yaw mechanism support structure, the yaw mechanism rotating support being configured to rotate about a first axis that is perpendicular to the upper surface of the yaw mechanism support structure.
 21. The lattice tower of claim 18, wherein the turbine longeron support frame is further configured to support the electrical generator, the electrical generator being coupled to a shaft.
 22. The lattice tower of claim 18, further comprising a nacelle housing the electrical generator.
 23. The lattice tower of claim 20, wherein the interface comprises at least one of: at least two wheels to transfer turbine loads to the track; at least a yaw actuator and yaw locking mechanism; a dampener element; and at least a pinion gear and a toothed track
 24. The lattice tower of claim 18, further comprising a power cable passageway defined in the yaw mechanism rotating support.
 25. The lattice tower of claim 18, wherein the wind energy turbine is operable with the plurality of rotor blades positioned downwind of the support platform. 